The addition of hydrazine compounds to silver halide photographic emulsions and developers has been described in U.S. Pat. No. 3,730,727 (a developer in which ascorbic acid and hydrazine are combined), in U.S. Patent 3,227,552 (hydrazine is used as an auxiliary developing agent for obtaining direct positive color images), in U.S. Pat. No. 3,386,831 (.beta.-monophenyhydrazides of aliphatic carboxylic acids are included as stabilizers for silver halide sensitive materials), in U.S. Pat. No. 2,419,975, and by Mees in The Theory of Photographic Process, third edition, (1966), page 281.
From among these literature references, the fact that high contrast negative images can be obtained by adding hydrazine compounds has been disclosed in particular in U.S. Pat. No. 2,419,975.
In the same patent specification it is disclosed that photographic characteristics which have a very high contrast with a gamma (.gamma.) value exceeding 10 can be obtained if hydrazine compounds are added to a silver chlorobromide emulsion and the material is developed in a high pH developer at a pH value of 12.8. However, a strongly alkaline solution of a pH approaching 13 is susceptible to aerial oxidation and is unstable, and it will not stand-up to long term storage or use.
Attempts have been made to form high contrast images by developing silver halide photosensitive materials which contain hydrazine compounds in developers of a lower pH.
Methods of processing in which development is carried out in a developer of a pH of not more than 11.0 using sensitive materials which contain nucleation development accelerators which have groups which are adsorbed on to silver halide emulsion grains and nucleating agents which have similar adsorption groups have been disclosed in JP-A-1-179939 and JP-A-1-179940. (The term "JP-A" as used herein signifies an "unexamined published Japanese patent application".) However, when compounds which have adsorbing groups are added to a silver halide emulsion there may be a loss of photosensitivity if a certain critical amount is exceeded, development may be inhibited or the action of other useful additives which are adsorbed may be impeded. So the amount which is used is limited, and satisfactory high contrast properties cannot be realized.
Hydrazine compounds which have ethylene oxide repeating units and hydrazine compounds which have pyridinium groups have been disclosed in U.S. Pat. Nos. 4,998,604 and 4,994,365. However, as is clear from the illustrative examples provided, the high contrast properties are inadequate and it is difficult to obtain the D.sub.max which is required and high contrast under practical development processing conditions.
Furthermore, with nucleation type high contrast sensitive materials in which hydrazine derivatives are used, the variation in photographic properties which accompanies any change in developer pH is considerable. The developer pH varies greatly, being increased by aerial oxidation of the developer and concentration due to evaporation of water and decreased by the absorption of carbon dioxide from the air for example. Hence, attempts have been made to reduce the developer pH dependence of photographic performance.
As mentioned above, it has not been possible to obtain a sensitive material which exhibits satisfactory high contrast properties even when processed in a developer of a pH less than 11 and with which the developer pH dependence of photographic performance is slight.
More precisely, the dot to dot sensitive materials (contact sensitive material) which are used in light rooms make use of a silver halide emulsion in which non-chemically sensitized silver chloride is used for the photosensitive layer. But even if the above hydrazine derivatives are used, the contrast is not hardened and there is the problem that if the contrast is hardened then the developer pH dependence is considerable. Moreover, in a contact sensitive material system, dyes are added to the photosensitive emulsion layers and other hydrophilic colloid layers to provide increased safety when the materials are being handled under fluorescent lighting from which the UV light has been filtered, and it is difficult to increase contrast because increased contrast is impeded by these dyes.